How to Estimate Soybean Yield

Harvested soybeans with some in shell

Before your combine even comes out of the shed, you’re probably trying to guess what the yield monitors and weigh wagons will report at the end of harvest. That’s good. The time to start planning for next year is right now.

Soybeans are arguably the most difficult crop to estimate yield, but there are ways to get more accurate estimates and evaluate otherwise unseen disease and insect pressure for next season.

A Simpler Way to Estimate Yields

As Growing Louisiana reports, a recently introduced, formula may alleviate some frustration while increasing accuracy of soybean yield estimates. Developed by Purdue University, this estimating method evaluates just 1/10,000th of an acre, instead of the typically recommended 1/1,000th of an acre.

Of course, by the time you’re in the combine, this year’s yield is set. The final yield results are determined through yield monitors and weigh wagons. But what you can do is watch the plants entering the grain table for indicators of pressure that developed after canopy when they were too large for you to scout. Those observations can help you make decisions for next year, as you talk with your seed dealer about what worked and what didn’t.

When harvesting this year’s crop, you can take steps to help prevent disease and insect infestation for next year as well.

Disease Observations

When frogeye leaf spot is present, symptoms typically appear on the leaves during the reproductive stages. Mild cases might go unnoticed and will not have a significant effect on yield. Given the right environmental conditions, however, frogeye leaf spot can escalate quickly.

It’s likely you would catch frogeye leaf spot in-season. During harvest, though, occasionally step out of the cab to investigate the soybean pods themselves for disease symptoms.

While this disease most commonly infects leaves, frogeye leaf spot can also cause lesions on stems and pods. Pod lesions, as described by Purdue University, are reddish-brown and slightly sunken. The disease can even spread through the pod walls and negatively affect the seed itself.

If you suspect frogeye leaf spot is present in your field, consult your local agronomist or retailer.

Planned fungicide applications at R3 have become a common practice for the management of frog eye leaf spot, but application as early as R2 may be needed under the appropriate environmental conditions. When selecting a fungicide product it is important to choose mixture products with two effective modes of action like Bayer’s Stratego® YLD. Due to the spread of strobilurin resistant frogeye leaf spot single mode-of-action products may not control the disease.

Insect Infestations

Soybean plants typically lose color and drop their leaves as harvest approaches. If you find yourself driving into a patch of brown pods on green stems this fall, you might have a case of green stem syndrome on your hands. Alternatively, you might hear it referenced as green bean syndrome.

Green stem syndrome reduces yield by aborting pods. It also makes harvest itself difficult by clogging equipment. Soybean viruses and environmental conditions can cause the syndrome, so can the bean leaf beetle and stinkbugs. The University of Arkansas suggests budworms are contributors too. 

As you investigate the cause and try to prevent green stem syndrome next year, one consideration should be your insecticide choice. Proper insect and worm control reduces the odds of green stem syndrome reoccurring next year.

Weed Control

Perhaps the easiest observation to make during harvest is that of weed escapes. They might have popped up near or at crop canopy and at a time when you thought you no longer needed to scout. Weeds or weed trash between the rows is an indicator of weed escapes. Whether or not these weeds are resistant to your herbicide, you might need to consider using an herbicide with a different mode of action next year. 

Are you also harvesting corn this year? We compiled some information on what to look for during that harvest, too.

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